The invention relates to the field of archery. More specifically, the invention relates to a short compound bow.
Archery bows have been known for centuries. Compound bows are a relatively recent development. It is widely believed that Holless W. Allen introduced the first one in 1967. The early compound bows included an eccentric wheel or cam, which provided a lesser pull weight (or let-off) at full draw than the maximum weight applied at an intermediate draw position. Thus, the compound bow stores a substantial amount of energy without requiring the archer to hold the maximum draw weight while aiming or waiting for a clear shot opportunity.
The technology of compound bows has evolved since Mr. Allen""s initial designs, including attempts to reduce the overall bow length. A short length makes carrying and handling the bow less cumbersome, a particular advantage in a blind or tree stand. However, attempts to shorten compound bows have met with problems because reducing the bow length tends to amplify certain forces acting on and within the bow. One such force is the torque caused by small angle differences between the grip/hand pressure and the draw line. Torque can cause unintended bow movement when the string is released, with consequent loss of accuracy.
Another consideration unique to compound bows is the need to displace the power cables away from the plane of the bowstring. Each power cable connects one end of the bowstring to the opposite limb through a pulley. Without some means of moving the power cables to the side, they would interfere with the travel of the bowstring and the arrow. Thus, cable guards have been developed to move the power cables to one side. Although these cable guards prevent interference with the arrow, the angle of displacement between the power cables and the plane of the bowstring at the pulleys creates another torque on the bow. In bows with a long bow length, measured axle to axle, the displacement angle is relatively small and, therefore creates little torque. However, as the length of the bow is decreased and the displacement distance of the power cables remains constant, the angle becomes larger and more torque is created.
Because torque is a hindrance to accuracy, efforts to reduce the length of compound bows have compromised accuracy. Although axle to axle length for hunting compound bows has dropped from the 40-inch range to closer to 30 inches, attempts to reduce the length of the bow to less than 30 inches have resulted in a trade-off in accuracy.
This invention relates to a well-balanced and accurate compound bow having a very short axle to axle length, a relatively long brace height and a relatively short power stroke. The bow includes a unique riser having a forwardly disposed grip, a rearwardly disposed portion extending generally vertically which makes up most of the riser length, and a limb-engaging portion extending forwardly from each end of the vertically extending portion a sufficient distance so that the forward edges of the limb-engaging portions are substantially in vertical alignment with the forward edge of the grip. A flexible resilient limb is connected to the riser at each limb-engaging portion. The limbs extend rearward at a steep angle to the vertical axis of the bow. The bow further includes a pulley mounted on an axle at the unsupported end of each limb, and a bowstring and power cable system associated with the pulleys.
The above-described configuration provides the compound bow with a center of mass above and rearward of the grip, and, therefore, a vertical axis of balance rearward of the grip. Because the limb engaging portions of the riser are substantially in vertical alignment with the grip, the vertical axis of balance is also rearward of the limb-engaging portions. The location of the vertical axis of balance relative to the grip and limb-engaging portions imparts excellent balance to the bow when it is drawn and released. The enhanced balance allows the limbs to be configured at a relatively steep angle from a vertical line drawn from the back of the grip. The steeply angled limbs, in combination with the size and configuration of the riser, provide a short overall bow length, as measured axle to axle, a relatively long brace height and a relatively short power stroke. The enhanced balance of the bow permits accurate shooting of fast, short arrows, despite the short bow length. Thus, the present invention provides a short compound bow with excellent accuracy and arrow speed.
The term xe2x80x9cbellyxe2x80x9d used in connection with a bow riser means the surface of the riser, or portion of the riser, that is closest to the archer user when holding the bow in the pre-draw position.
The term xe2x80x9cbackxe2x80x9d used in connection with a bow riser means the surface of the riser, or portion of the riser, that is farthest from the user when holding the bow in the pre-draw position.
The term xe2x80x9cbrace heightxe2x80x9d means the distance from the belly of the grip at its deepest point to the bowstring when not drawn.
The term xe2x80x9cdraw lengthxe2x80x9d is the distance from the belly of the grip at its deepest point to the bowstring (at the nock) when drawn.
The term xe2x80x9cpower strokexe2x80x9d represents the distance the nock is displaced when the bowstring is drawn.
The term xe2x80x9crearwardlyxe2x80x9d refers to a direction that starts from the back of the riser and progresses toward the bowstring. xe2x80x9cRearwardxe2x80x9d of an element or position is the state of being in a vertical plane that is located farther away from the back of the riser than is the element or position.
The term xe2x80x9cforwardlyxe2x80x9d refers to a direction that starts from the bowstring and progresses toward the back of the riser. xe2x80x9cForwardxe2x80x9d of an element or position is the state of being in a vertical plane that is located farther away from the bowstring than is the element or portion.
The term xe2x80x9cpulleyxe2x80x9d is meant to include cams, wheels and eccentric wheels, or positions thereof.
The term xe2x80x9cvertical axis of balancexe2x80x9d is a vertical line through the center of mass of a bow when the bow is held upright.
The term xe2x80x9cplane of the bowstringxe2x80x9d is used to indicate the plane through which the bowstring travels as it is drawn and released. An arrow also travels through the plane of the bowstring.